1. Field of the Invention
The present invention relates to an image taking apparatus usable in a television camera, a video camera, a television lens, a video lens, and the like which perform an automatic focus detection and focusing control (hereinafter referred to as an AF control).
2. Related Background Art
In recent years, the AF control is indispensable in image taking apparatuses such as video cameras for consumers. In such a kind of AF control, a prevailing method is an automatic focus detecting method in which a signal in conformity with a sharpness of an object is extracted from a pickup signal, and evaluated to execute a focus detecting operation of an optical system.
An operation example of that AF control method will be described with reference to FIG. 3.
In FIG. 3, reference numeral 600 designates a camera having a lens unit which is incapable of detachable attachment to a camera unit. Reference numeral 102 designates an evaluation value generating unit for extracting a sharpness evaluation value from a video signal output from a processing unit 202 (described later). Reference numeral 103 designates an AF drive controlling unit for generating a motor control signal such that the sharpness evaluation value generated by the evaluation value generating unit 102 can be maximized. Reference numeral 105 designates a motor which is driven under the control of the AF drive controlling unit 103. Reference numeral 106 designates a focus lens movable in its optical-axis direction by the drive of the motor 105. Reference numeral 201 designates a CCD. Reference numeral 202 designates a processing unit for processing an output signal of the CCD 201 and shaping it into a format such as an NTSC signal. Reference numeral 203 designates a recording and reproducing unit for recording a video signal of an output from the processing unit 202 in a record medium, and reproducing a video recorded in the record medium.
In the above structure, a light beam transmitted through the focus lens 106 is imaged on a pickup surface of the CCD 201, and the image is sampled and held, and input into the processing unit 202 after photoelectrically converted by the CCD 201. The processing unit 202 processes the input signal into a video format, such as the NTSC signal, and outputs it into the evaluation value generating unit 102 and the recording and reproducing unit 203. The video signal output to the evaluation value generating unit 102 undergoes a filtering process and the like in the evaluation value generating unit 102, and the sharpness evaluation value relevant to a frequency component of the video is thereby generated by a unit of a vertical synchronization period of the video signal. The thus-generated sharpness evaluation value is output into the AF drive controlling unit 103. The AF drive controlling unit 103 generates the motor control signal for moving the focus lens 106 to a position whereat the sharpness evaluation value becomes maximum, while driving the motor 105 and successively comparing the sharpness evaluation values by a unit of the vertical synchronization period. The AF drive controlling unit 103 thus drives the motor 105 to move the focus lens 106 to its in-focus state. The recording and reproducing unit 203 records the output of the processing unit 202 in the record medium, and reproduces the recorded video image.
A driving example of such an AF operation will be described. Initially, judgment of a driving direction is performed by judging if the in-focus state is on a far-distance side or a short-distance side relative to a current position of the focus lens 106. In this judgment, the focus lens is moved by a small amount, and the judgment is performed based on a change of the sharpness evaluation value at the moved position. After that, the focus lens 106 is moved at a certain rate according to the result of the driving direction judgment to detect a peak value of the sharpness evaluation value. This is a so-called hill-climbing method. The moving direction of the focus lens 106 is reversed after the peak value is detected, and the focus lens 106 is moved by a unit of a small amount, and guided such that the sharpness evaluation value can be maximized. This is called a peak judgment. After the peak judgment, the sharpness evaluation value continues to be read, and the read value is compared with a value immediately after the peak judgment. Upon detection of variation of the value, the AF operation is re-started.
Such a video AF operation in a camera system adopting an interchangeable lens structure is disclosed in EP-762742-A2.
Further, there exist a group of products (hereinafter referred to as a remote system) for remote operation uses to be used for monitoring, bridal image taking and the like, such as television cameras, video cameras, television lenses, and video lenses. In such a remote system, no AF control is installed, and its structure is constructed such that an operator can operate a switch, a volume switch and the like installed in a remote control unit capable of remote operation, and zooming, iris stop and focusing can be remotely controlled.
In the remote system, an electrical interface is established between the remote control unit and the camera, and twelve (12) pins are assigned to instruction signals of zooming, iris stop and focusing, control mode signals (switchover between a speed control and a position control), electrical power source, ground and so forth, respectively. Thus, there are no vacant pins in the system.
An operation example of the remote system will be described with reference to FIG. 4. Portions designated by reference numerals 600, 201 to 203, 105 and 106 in FIG. 4 are those discussed above with reference to FIG. 3, and accordingly descriptions thereof are omitted.
In FIG. 4, reference numeral 400 designates a remote control unit for supplying to the camera 600 instruction signals for controlling a zoom lens portion (not shown), an iris stop portion (not shown), and the focus lens 106 provided in the camera 600, and a switchover signal for performing the switchover between controls of the focus lens 106 by the speed control and the position control. Reference numeral 500 designates a remote control cable connecting the camera 600 and the remote control unit 400. Reference numeral 107 designates a remote control input terminal for inputting the instruction signal and the switchover signal from the remote control unit 400 into the camera 600 therethrough. Reference numeral 109 designates a manual focus (hereinafter referred to as MF) drive controlling unit for generating a motor control signal for driving the motor 105 from an MF instruction signal from the remote control unit 400. Reference numeral 110 designates an S/P switchover signal judging unit for outputting to the MF drive controlling unit 109 an S/P switchover instruction signal for instructing whether the control of the focus lens 106 should be executed by the speed control or the position control based on at S/P switchover signal output from an S/P switchover signal inputting unit 402.
In the remote control unit 400, there are arranged an MF instruction signal generating unit 401 for generating the MF instruction signal, which is comprised of the switch, the volume switch and so forth, the S/P switchover signal inputting unit 402 for performing the switchover of the control of the focus lens 106 between the speed control and the position control, and a remote control output terminal 405 for outputting to the camera 600 the instruction signal and the switchover signal from the remote control unit 400.
In the above-discussed structure, in accordance with an operation of the MF instruction signal generating unit 401, the MF instruction signal proportional to this operation is output from the MF instruction signal generating unit 401, and is input into the MF drive controlling unit 109 through the remote control output terminal 405, the remote control cable 500, and the remote control input terminal 107. Further, the S/P switchover signal for performing the switchover of the control of the focus lens 106 between the speed control and the position control is output from the S/P switchover signal inputting unit 402, and is input into the S/P switchover signal judging unit 110 through the remote control terminal 405, the remote control cable 500, and the remote control input terminal 107. The S/P switchover signal judging unit 110 judges by which of the speed control and the position control the control of the focus lens 106 should be executed, and its judgment result is output to the MF drive controlling unit 109 as the S/P switchover instruction signal. In the MF drive controlling unit 109, where the S/P switchover instruction signal is a signal for performing the control of the focus lens 106 by the speed control, the MF instruction signal is treated as a speed control instruction signal, and the motor control signal for driving the motor 105 at such a speed as instructed by the MF instruction signal is generated. The motor 105 is accordingly driven to move the focus lens 106. On the other hand, where the S/P switchover instruction signal is a signal for performing the control of the focus lens 106 by the position control, the MF instruction signal is treated as a position control instruction signal, and the motor control signal for driving the motor 105 to such a position as instructed by the MF instruction signal is generated. The motor 105 is accordingly driven to move the focus lens 106.
In the above-discussed conventional example, however, where the AF control is installed in the remote system, there are no vacant pins at the electrical interface between the remote control unit and the camera. It is therefore impossible to assign to the electrical interface the switchover signal for performing the switchover of the drive of the focus lens between the AF control and the MF control from the remote control unit, and provide in the remote control unit the switchover unit for performing the switchover of the drive of the focus lens between the AF control and the MF control.